A large number of infant formulas are based on proteins from cow's milk. Infants who are truly allergic to milk protein require infant formulas wherein the proteins are extensively hydrolyzed to contain a minimum of residual molecular structures. For non-allergic infants, an infant formula with reduced antigenicity has prophylactic benefits in that it can delay or prevent sensitization which could otherwise lead to clinical symptoms of allergy. The allergenic potential of cow milk-protein based formulas can be reduced by protein hydrolysis.
To ideally meet the composition of human milk, the cow milk protein in infant formulas should contain both whey protein and casein in an appropriate ratio. While a number of products based on intact milk protein meet a desirable whey protein to casein ratio, almost all of the commercially available partially hydrolyzed formulas are based on 100% whey protein.
Processes for preparation of partial hydrolysates described in the literature generally involve multi-step hydrolysis and physical separations after the hydrolysis to eliminate enzymes and/or residual proteins. Most processes also involve constant pH control during hydrolysis. Also, unless another process step is introduced, the resulting hydrolysate will usually have a high level of salts which can pose formulation problems in the infant formula, the level of minerals of which are usually regulated at a certain level.
U.S. Pat. No. 5,039,532 describes two steps of enzymatic hydrolysis to attain a hydrolysate of desired characteristics. It also describes preparation of an infant formula which is ultra-high temperature (UHT) sterilized. U.S. Pat. Nos. 4,293,571 and 4,981,704 both describe partial hydrolysates prepared using pancreatic enzymes which involve post-hydrolysis membrane processes to separate out the residual proteins and enzymes.
A common characteristic of protein hydrolysates, particularly hydrolysates containing casein, is bitter flavor development putatively due to liberation of peptides with hydrophobic end groups. Moreover, the emulsifying property of proteins generally is also decreased as the degree of hydrolysis increases. Japanese Patent 1160458 describes a milk protein hydrolysate (5-20% hydrolyzed) which is surface active and shows emulsifying activity in foods such as ice cream and whipping cream. However, in products such as liquid infant formulas which undergo sterilization processes, further denaturation of the protein hydrolysate renders it less functional in an emulsion. This is manifested in the product as a separation into a serum and cream layer. The high temperature-short time conditions of UHT sterilization is commonly preferred to conventional retort sterilization to prevent the adverse exposure to heat.
Thus, it would be highly desirable to have a partial protein hydrolysate which has reduced antigenicity, has a whey protein to casein ratio which provides a protein composition similar to human milk, has improved taste, and/or has improved emulsifying activity.